Vaillant F75 Fault: What It Means and How to Fix It
The F75 error on a Vaillant boiler points to a pump or water pressure sensor problem. Here's what it means — and when to call a Gas Safe engineer.
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Upfront cost — no obligation If your Vaillant boiler is showing an F75 fault code, it has detected a problem with the water pressure sensor or the pump — specifically, it isn’t sensing the expected change in pressure when the pump runs. It’s one of the more common Vaillant faults, and while the cause is usually a failed pump or pressure sensor, it needs a Gas Safe registered engineer to diagnose and repair safely. This guide explains what F75 means and what to do.
What does F75 mean?
On Vaillant ecoTEC and similar boilers, F75 means the boiler cannot detect a rise in water pressure when the pump starts. The boiler expects the pressure sensor to register a change as the pump kicks in; when it doesn’t, it logs F75 and shuts down to protect itself. The most common causes are a faulty or seized pump, a failed pressure sensor, low system pressure, or trapped air in the system.
On Vaillant ecoTEC and similar boilers, F75 means the boiler cannot detect a rise in water pressure when the pump starts.
What you can safely check yourself
There’s one thing a homeowner can safely check: the pressure gauge. If it reads below about 1 bar, low pressure may be contributing, and topping up the system pressure using the filling loop (following your boiler’s manual) sometimes helps. You can also try the boiler’s reset once. Beyond that — checking or replacing the pump or sensor — is a job for a Gas Safe engineer. Do not attempt to dismantle the boiler.
There’s one thing a homeowner can safely check: the pressure gauge.
When to call an engineer
If repressurising and a single reset don’t clear F75, or the fault returns, call a Gas Safe registered engineer. A persistent F75 almost always means the pump or pressure sensor needs replacing — both internal repairs that must be done by a registered professional. Continuing to reset a boiler that keeps faulting won’t fix the underlying problem.
If repressurising and a single reset don’t clear F75, or the fault returns, call a Gas Safe registered engineer.
We fix Vaillant F75 faults across East London
Gas First repairs Vaillant boilers throughout East London and Essex, and F75 is a fault we see regularly. We carry common Vaillant pumps and sensors, so we can often diagnose and repair on the same visit. Tell us it’s an F75 when you call and we’ll arrive prepared.
Gas First repairs Vaillant boilers throughout East London and Essex, and F75 is a fault we see regularly.
Frequently Asked Questions
Can I fix an F75 fault myself?
You can safely check the pressure gauge and top up pressure via the filling loop, and try one reset. Repairing the pump or pressure sensor must be done by a Gas Safe registered engineer.
What usually causes F75 on a Vaillant?
Most often a failed pump or water pressure sensor, sometimes combined with low system pressure or trapped air.
Will resetting clear the F75 fault?
A reset may clear it temporarily, but if the underlying pump or sensor is faulty it will return. Repeated resets aren't a fix.
How much does it cost to fix an F75 fault?
It depends on whether the pump or the pressure sensor needs replacing. We diagnose the fault first and explain the cost before carrying out any work.
Is an F75 fault dangerous?
The boiler shuts down to protect itself, so it's not usually an immediate danger, but you'll have no heating or hot water until it's repaired.
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